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Salt-Sediment Interaction in Sable Sub-Basin, Nova Scotia (Canada)


The Sable Sub-basin is a complex geological sub-basin located in the Central slope of the Scotian margin. It is characterised by an intricate interplay between structural inheritance, salt tectonics and synkinematic sedimentation. One challenge faced during deep water exploration in the area was to understand reservoirs distribution along the slopes. Part of the challenge is the difficulty in identifying preserved canyons or long-lasting sediment conduits that connect the shelf to the slope. We present here an update on the current view on the evolution of the Central Slope sedimentary system through time in response to salt tectonics. For this purpose, we use newly reviewed and reinterpreted seismic data and related thickness maps on the Central Scotian slope. Results show that the Central Scotian slope can be subdivided in three tectonostratigraphic compartment. The first phase of deformation occurred in the northeast of the study area during Callovian-Tithonian interval, with rapid salt migration over the Alma ridge leading to the creation of the Banquereau Synkinematic Wedge (BSW). Post BSW mechanical adjustment allows the accumulation of a thick Valanginian interval against the main listric faults. The BSW acts as a topographic high and forces the sediment to flow toward the central part of the study area. In the central and southwestern part of the Sub-basin, salt deformation starts at the end of the Jurassic and intensifies shortly after the base Cretaceous unconformity in response to the deposition of the Missisauga Fm. The initiation of a salt canopy by the Hauterivian time disrupts the sediment supply to the deeper part of the basin, and sediment starts to pile up ahead of the salt wall. During the Aptian–early Cenomanian salt canopies are well developed. The significant sediment load over the salt canopy leads to the formation of numerous short lived intra salt mini-basins. Additionally, due to the amount of growth fault at the shelf edge, several mini–basins appear to form on the upper slopes which would tend to trap sandstones early on. Because of the intense salt tectonics, canyons do not last very long and sediment conduits are perpetually evolving. The southwestern part of the study area is characterised by the development of a large roho system. Salt movements and withdrawal creates a large turtle back structure bordered by two large permanent sediment conduits. These conduits allow a direct connection between the shelf to the basin.